Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants include solid material known as particulate matter or soot. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of particulate matter emitted from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
One method implemented by engine manufacturers to comply with the regulation of particulate matter exhausted to the environment has been to remove the particulate matter from the exhaust flow of an engine with a device called a particulate trap or diesel particulate filter. A particulate trap is a filter designed to trap particulate matter and typically consists of a wire mesh or ceramic honeycomb medium. Although initially the particulate trap may adequately remove particles, the use of the particulate trap for extended periods of time may cause the particulate matter to build up in the medium, thereby reducing the functionality of the filter and subsequent engine performance.
The collected particulate matter may be removed from the filter through a process called regeneration. To initiate regeneration of the filter, the temperature of the particulate matter trapped within the filter must be elevated to a combustion threshold, at which the particulate matter is burned away. One way to elevate the temperature of the particulate matter is to inject an energy source, such as diesel fuel, into the exhaust flow of the engine and ignite the injected fuel. Ignition is typically achieved by way of a spark plug.
After the regeneration event, the supply of fuel is shut off. However, some fuel may remain within the fuel injector or the fuel lines that direct fuel to the injector. This remaining fuel, when subjected to the harsh conditions of the exhaust stream, may coke or be partially burned, leaving behind a solid residue that can restrict or even block the fuel injector. In addition, it may be possible for particulate matter from the exhaust flow to enter and block the injector. For this reason, it may be necessary to periodically purge the injector of fuel and/or any built up residue or particulate matter between regeneration events.
One method of purging a fuel injector is described in U.S. Pat. No. 4,533,316 (the '316 patent) issued to Takino et al. on Aug. 6, 1985. Specifically, the '316 patent discloses a combustion apparatus of a fuel vaporizing type, wherein fuel (kerosene) is supplied to a fuel injector for vaporization, and the vaporized fuel is fed to a burner via a gas nozzle for combustion. Combustion is achieved when the gas fuel from the fuel injector is fired with a spark discharge originating from an ignitor.
While the kerosene is being vaporized within the fuel injector of the '316 patent, the kerosene is reduced slowly into tar due to polymerization of molecules, microscopic residues (impurities), etc. As the tar is attached and deposited in the vaporizing core of the fuel injector, a passage for the vaporized kerosene is gradually choked with the tar, so that the proportion of the vaporized oil gas decreases and the rate of combustion slows down, causing a faulty combustion state. To solve this problem, the combustion apparatus is characterized by a heater for removing tar at a high temperature, which is attached within the fuel injector.
The heater is seated tightly on a side wall of the fuel injector body and constantly biased toward the fuel injector body by the force of a spring. During a normal combustion state, the heater operates so as to maintain the interior of the fuel injector at a temperature of 240 degrees to 280 degrees C. under the control of a temperature-monitoring element (typically, a positive characteristic thermistor) and an electronic control. When it is desired to conduct a fuel-empty burning (to remove tar), the temperature-monitoring element is short-circuited, interrupting operation of the electronic control, and establishing a continued heating mode. Consequently, the temperature in the fuel injector reaches 500 degrees C. and tar attached to the vaporizing cylinder of the fuel injector is thermally dissolved and finally removed. When fuel-empty burning is effected, the residual fuel in an associated fuel tank should be removed.
Although the fuel injector of the '316 patent may benefit from the tar removing process described above, the gain may be expensive. In particular, the fuel injector of the '316 patent requires a heater for cleaning the injector and a separate ignitor for normal operation. Having a separate heater and ignitor may increase component cost and assembly time. Furthermore, because the '316 patent recommends the removal of the fuel from the fuel tank, operation of the injector may be periodically interrupted. The fuel injector of the present disclosure solves one or more of the problems set forth above.